Caveats Regarding CIAO and Archive Data

Aspect

Tom Aldcroft
06/22/09

Caveats

Aspect offset of 0.4 arcsec in early 2007

Applicability

Chandra observations taken after 2006-Dec-10 and processed on or before 2007-May-14.

Issue

These observations are subject to a systematic aspect offset of approximately 0.4 arcsec. This is believed to be the result of a changed thermal environment following the procedure to cool the ACA CCD from -15C to -19C that took place between late Nov-2006 and early Jan-2007. New calibration files to correct this offset were installed effective 2007-May-14 and affected observations were reprocessed to remove the offset.

Resolution

If the processing date in data files for applicable observations is before 2007-May-14 then observers should retrieve the latest files from the Chandra archive. These will have the current aspect calibration applied.

Last modified: 06/22/09

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